DESCRIPTION: The biomechanical and physiological processes associated with the development of cumulative spinal disorders due to long term application of static and repetitive occupational loads to the spine will be investigated. It is hypothesized that spinal tissues, when exposed to creep / elongation due to repetitive or static loads, cause desensitization of sensory receptors within and consequent loss of reflexive muscular activity, rendering the spine exposed to instability and potential injury. Full recovery of the creep / elongation and muscle activity while resting between sequential work periods may not be possible, allowing the cumulative increase of residual creep / elongation over time to develop long lasting neuromuscular disorders. A five year experimental research program consisting of the in-vivo feline model will systematically explore the relationship between cumulative loads applied to spinal ligaments, discs, etc., in sequential static and cyclic work / rest periods as well as the following recovery in eight hours of rest to the activity level of paraspinal muscles and the disorders in their functions. The results of this research will provide strong insights into biomechanics and the neurophysiology of low back disorders in common occupational activities; provide an insight to the effect of sequential cumulative loads and daily rest on development of spinal disorder in the short and long term; and delineate optimal work / rest periods that may minimize or prevent the development of low back disorders in the most common occupational activities.